Apparatus for and method of applying tin to metallic sheets



Dlec. 3l, 1935. N|EMAN 2,025,768

APPARATUS FOR AND METHOD OF APPLYING TIN TO METALLC SHEETS Filed Aug. 15, 19:51 sheets-sheet 1 De@ 31 1935- H. w. NIEMAN 2,025,768 'APPARATUS FOR AND METHOD OF APPLY'ING TIN TO METALLIC SHEETS Filed- Aug. l5, 1931 2`Sheets-Sheet 2 v&f

gwventoc Patented Dec. 3l, 1935 PATENT OFFICE APPARATUS OR AND IVIETHOD OF APPLY- ING TIN T METALLIC SHEETS v Henry W. Nieman, Bethlehem, Pa., assignor to Bethlehem Steel Company, a corporation of Pennsylvania Application August 15, 1931, Serial No. 557,406

11 Claims.

This invention relates to methods ofand apparatus for applying tin coatings to the surfaces of metallic sheet strips or the like.

Various types of machines are now employed 5 for the purpose of applying tin coatings to metallic sheets and are well-known in the metal working industry. Generally speaking, each such appliance includes a receptacle, known as a tin pot, through which the sheet is passed, a bath of molten tin being contained in the tin pot, and the sheet, in passing through this bath of molten tin,

` picking up a sufcient amount of the tin to adequately cover and coat its surfaces. It has been found diicult, however, to apply a perfect tin coating in most instances, particularly where large quantities of metal, such as very long strips, are continually passed vthrough the tin bath, as the molten tin becomes gradually contaminated with impurities known as particles of scrui or dead metal which adhere to the sheet when it passes through the bath and which, when they pass through the tinning rolls, result in roughen- `in g or disiigurement of the surfaces.

Solid impurities which tendto collect in a tin bath and to contaminate the same may be divided into three classes. The rst class comprises light particles of carbon and dirt which settle through the palm oil, which is universally maintained above the surface of the tin, and rest on the top surface of the body ofmolten tin. The second class includes particles, mainly iron, which amalgamate with the tin and settle down to the bottom of the tin pot. 'Ihe third class comprises particles which partially amalgamate but, owing to their small size, porosity, or admixture with lighter constituents, accumulate just below the top surface of the tin, forming a layer with an indefinite lower boundary.

The lighter particles, which settle downwardly 40 through the layer of palm oil, are easily prevented from reaching the surface of the tin by means of shields such as are well-known in the art. However, the light and heavy impurities in the tin bath are difcult to handle and have up until this time constituted a serious obstacle in the tinning processes now in commercial use. Thus, these particles in the tin bath diier in specific gravity only slightly from that of the tin itself so that they tend to float around in the tin and, even when they ultimately reach either the upper surface of the tin layer or fallto the bottom of the tin pot, are very easily dislodged by any current which may exist in the body of the molten tin and then carried vinto contact with the sheets passing through the apparatus. Heretofore,

(Cl. {l1-70.2)

therefore, it has generally been considered essential to provide a relatively large tin bath and to avoid agitation of the bath. Even by taking such precautions, however, satisfactory results have not been realized, particles of heavy material in the portion of the bath directly above the strip contacting with the strip as they fall and the lighter particles below the strip tendingto rise and foul the strip on coming in contact therewith. l0

In accordance with the present invention, I provide a ldefinite circulation of the tin in the tin pot and also provide means for continuously cleaningv the circulating tin and for causing the stream of molten tin thus cleaned to come in l5 contact with the metallic sheet passing through the tin pot. By the method just suggested and by suitable apparatus which will hereinafter be more fully described, it is possible to pass a metallic sheet through a tin pot without having 20 the sheet come in contact with any appreciable number of solid particles which tend to interfere with the perfection of the tinning process.

The invention is not limited in its broader aspects to any particular type of apparatus, and 25 the method may be carried out in tin pots which vary widely in design and arrangement of their component elements. 'I'hat form of apparatusv which is illustrated in the accompanying drawings is set forth by way of example only. The 30` method of and means for cleansing the tin may also be used quite independently of the actual tinning operation.

In the drawings: l

Figure 1 shows, in longitudinal section, a tin 35 pot which is generally of a type now in common use but in which certain changes have been made in order to facilitate carrying out the improved process;

Figure 2 is an end View of the tin pot, partially 40 broken away to show the interior, and also showing in elevation, affixed thereto, the tin cleaning apparatus; and

Figure is an axial section through the tin cleaning apparatus. 45

The tin pot is indicated. generally at III and is seen to comprise a portion ID' adapted to contain a part of the bath of molten tin (indicated at II) and a small body of molten flux (indicated at I 2) the portion Ill' being in communi- 50V cation with the portion III,2 of the pot only through an elongated arcuate passageway I3 delined by the curved shields I4, I4. The portion I0' of the tin pot contains a portion of the tin bath, the level of the upper surface of which 55 vtively small apertures 36.

bath is indicated at I5, and also a relatively deep body of palm oil, the level of the upper surface of which body is indicated at I6. Guide rolls arranged' in pairs are indicated at II, by means of which the incoming sheet of metal, which is moving in the direction of the arrow A, is guided into the passage between the shields I4, and pairs of tinning rolls positioned in the palm oil -bath are indicated at |8,.these rolls engaging the sheet of metal after it has emerged from the tin bath and being intended to remove the surplus tin and to produce a thin uniform coating.

In the main, the arrangement of parts just described is well-known. In accordance with my invention, however, I provide transverse manifolds 20 horizontally disposed along the upper edges of the shields I, each of these manifolds being provided with series of apertures 2| directed toward the sheet of metal 22 passing between them.4 In the operation of the apparatus, molten tin is caused to flow through the manifolds 20 under light pressure and to be delivered in a large number of small streams through the apertures 2| against the surface of the metallic sheet. This tin has previously been purified by means hereinafter to be described, and the streams of tin, after lmpinging against the metallic sheet, join and iiow downwardly through the duct or neck between the shields I4, streams of clean tin therefore sweeping downwardly along the sheet 22 on both sides thereof and finally emerging into the main bath of ltin in the portion I0 of the tin pot. Hence it is clear that not only is the sheet of metal actually passing between the shields I4 in contact with pure, uncontaminated, molten tin but that this molten tin is flowing in streams directed oppositely to the direction of movement of the incoming metallic sheet, so that any impurities which may have come into contact with the sheet are washed off by the action of the flowing streams of tin. In this way impurities are prevented from clinging to the sheet which, when it reaches the tinning rolls |8, has a coating of pure tin. The resulting product presents an improved and practically perfect surface.

The means for purifying the tin will now be described. It will b'e noted in Figure 1 that there is present in the portion |Il2 of the tin pot, and below the level of the surface lof the tin, a tin off-take pipe 25. This pipe is also shown in Figures 2 and 3 and will be seen to lead to a point below the cylindrical casing 26 of the purification apparatus and there turns upwardly, passing through a hollow trunnion 26' mounted in a frame member 2'I and discharging into the bottom of a cylindrical drum 28. The drum 28 is mounted on trunnion 26' and hence is revolubly mounted in the frame member 21, and at the top of the apparatus a. second frame member 29 is provided through which a shaft 30 extends, this shaft having its upper end connected to a driving motor 3| and its lower end fixed in a spider 32 which bridges the reduced neck 33 extending axially from the upper end ofl cylinder 28. Cylinder 28 is therefore freely revoluble and is supported by frame members 2'I and `29 for free rotation by the electric motor 3|. Midway of the top and bottom of the cylinder 28 is a horizontal partition 35, which partition is provided with a plurality of spaced rela- Mounted upon the upper side of the partition and disposed coaxially with the cylinder 28 is a cylindrical block 31. The neck 33 terminates in an annular flange or lip 38 which extends laterally and in close proximity to an annular channel 39 surrounding the neck.

As may be seen from Figure 2 of the drawings, 5 the discharge end of the tin conduit 25 is positioned below the level of the upper surface of the tin bath in the compartment |02 of the tin pot, and hence there is. a tendency for the tin to ow from the tin pot into the lower compart- 10 ment of the rotatable drum 28. An annular shield 40, secured to the upper end of conduit 25, causes the tin to flow outwardly and onto the bottom of cylinder 28 as it emerges from the end of pipe 25 and prevents it from finding its 15 way down between the cylindrical inner `surface of trunnion 26 and the cylindrical outer surface ofthe pipe 25.

In the operation of the device, the cylinder 28 is rotated at relatively high speed, and the-20 tin flowing into the cylinder through pipe 25 is immediately thrown downwardly against the wall of the cylinder by centrifugal action. Ultimately a thick layer of tin is built up against this wall, and the inner surface of this tin layer 25 will occupy somey such position as indicated at 42. Naturallya quantity of the tin immediately flows through apertures 36 into the upper compartment, and when a sufliciently thick layer is built up in this compartment, as indicated by 30 the line 43, tin will begin to pass into the neck 33 and, inasmuch as this neck flares upwardly, will rise rapidly in the neck and ultimately be discharged over the ange 38 and into the annular stationary trough 39, from which trough 35 it will pass by gravity into the pipe 44. y

Pipe 44 is positioned above the manifolds 2|] and is connected to the ends of these manifolds so that the tin will iiow downwardly and into the manifolds, creating a pressure in the mani.- folds and causing the jets of tin to flow outwardly through orifice 2| and against the metal sheet 22 in the manner heretofore described. Due to centrifugal action, the particles or impurities which are lighter than the tinwill be 45 collected in the first compartment of the cylinder 28, being thrown toward the center of this l compartment so that they come to occupy positions in the inner layer of the body of tin contained in this compartment, such positions being indicated, for instance, at 46. These lighter impurities will be trapped in the lower compartment so long as the purifier remains in operation. The tin, still containing its heavier impurities, flows through the apertures 36 into the 55 upper compartment and will here be separated from such heavier impurities, which collect adjacent the wall of the cylinder, as for instance in a layer indicated at 41. The molten tin which ultimately flows upwardly through the neck 33 00 of the cylinder, has been separated from both its lighter and heavier impurities and is practically free from all impuritieswhatever. The partition 35 may be designated a baie for preventing iiow of the lighter impurities through the apparatus. 65 and the annular portion 28' of the top of the cylinder may be termed a bafile for blocking the passage of the heavier impurities.

-In order that sufcient heat may be imparted to the apparatus to prevent freezing of the tin, gas heating names vmay be provided. For instance, a gas conduit 5D positioned below conduit 25 may be provided with a plurality of apertures 5|, and the gas escaping through these apertures will provide heating ames 52 to'main- 75 tain the tin flowing through conduit 25 sufiiciently molten. Also the exterior surface of the cylinder 28 may be heated by gas flames 53 resulting from the combustion of gas issuing from apertures 54 in a gas manifold 55. To maintain a non-oxidizing or neutral atmosphere in the apparatus, particularly in the neck 33 and above the surface of the tin in trough 39, a neutral or reducing gas may be introduced into the apparatus above the upper level of the tin through a pipe 56. At 5l an overow pipe 4is indicated, by means of which any excess quantity of tin owing out from neck 33 may be returned to pipe 25. Normally the molten tin stands in this overflow pipe at the same level as the discharge end of conduit 25, with which it is in open communication. A

The tin cleaning apparatus is maintained in operation as long as the process of tinning isl carried on and is drained whenever the process is halted. It is simple in operation, having only one moving part, inexpensive to construct and operate, and emcient in operation. It will be observed that the centrifugal apparatus disclosed comprises not only a means for cleansing the tin `as it flows through but also a pump, inasmuch as it withdraws molten tin from the tin pot at one level and returns it at a higher level. As a pump, the apparatus may have various uses other than in connection with a tin pot or process of tinning, particularly in the handling of molten metal, and its design may be considerably modied inadapting it to various uses.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:-

1. The method of tinning by the use of a tin bath which comprises removing aportion of the molten tin from the bath, cleansing the same, and returning the cleansed tin to the bath in such manner that the surfaces of an object undergoing the tinning operation are swept by streams of the returning cleansed tin.

2. 'I'he method of tinning articles by the use of a tin bath which comprises continuously removing molten tin therefrom, cleansing the same, continuously returning the cleansed tin to the bath and simultaneously passing said articles through said bath.

3. 'I'he method of tinning comprising immersing an article to be tinned in a bath of relatively impure molten tin, removing said article from said bath and cleansing said article by a ow of relatively pure molten tin.

4. The method of tinning sheet material com prising passing said material through a tin bath, continuously removing molten tin from said bath. cleansing said tin and continuously returning the cleansed tin to the bath at points adjacent to the line of emergence of said sheet from said bath.

5. The method of tinning sheet material comprising immersing said material in a bath of relatively impure molten tin, removing said material from said bath, cleansing said material by a ow of relatively pure molten tin and passing said material through rollers maintained at a temperature above the melting point of tin.

6. Apparatus for tinning sheet material comprising a bath of moltenl tin, centrifugal means for continuously cleansing molten tin, means vfor continuously transferring molten tin from said bath to said cleansing means and from said cleansing means to said bath, and handling means operative simultaneously with all of the 5 above mentioned means for immersing in and removing said sheet material from said bath.

7. Apparatus for tinning sheet material comprising a. bath of molten tin, rollers for introducing said sheet material into said bath, rollers disposed above said bath for removing said sheet material from said bath, elongated nozzle means disposed below said second mentioned rollers and directed against said sheet material, centrifugal means for removing heavy impurities from 15 molten tin, centrifugal means for removing light impurities from molten tin, pump means, conduit means connecting said bath with said pump means, and with said first and second mentioned centrifugal means, and conduit means connecting said centrifugal means with said nozzle means whereby a ow of molten tin from said bath is forced in succession through said centrifugal means and said nozzle. means.

8. The process of coating a metal article with 25 a metal coating which comprises passing the article to be coated through a main bath of molten coating metal, discharging additional molten coating metal upon said article at a point abve the point where said article leaves said main 30 bath, said metal being discharged in a continuous stream into said main bath and enveloping the article to be coated at the point where said article leaves said main bath, whereby contact of said article and the metallic oxide on the sura5 face of said main bath is prevented.

9. The process of coating a metal article with a metal coating which comprises passing said article through a main bath of molten coating metal, discharging a continuous stream of like 40 coating metal upon said article at a point above the point where said article leaves said main bath, said metal being discharged in a continuous stream into said main bath and enveloping said article at the point where said article leaves said main bath, whereby the metallic oxide on the surface of the bath is prevented from coming into contact with the article being coated.

10. The method of tinning comprising immersing articles to be tinned in a bath of relatively impure molten tin, continuously removing portions of said bath, purifying said portions and continuouslycirculating saidl purified portions over said articles.

1l. The process of coating a metal article with 55 a metal coating which comprises passing said article through a main bath of molten coating metal, discharging a continuous stream of like coating metal upon said article at a point abovethe point where said article leaves said main bath, said metal being discharged in a continuous stream into said main bath and enveloping said article at the point where said article leaves said main bath, whereby the metallic oxide on the surface of the bath is prevented from coming into contact with the article being coated and maintaining a non-oxidizing environment about the point of discharge of said continuous stream into said main bath.

HENRY w. NmMAN. to 

